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• 28 years of sewage sludge application at low to moderate doses had a low effect on organic C concentration. • Soil organic C storage increased only at the highest dose (80 tons ha−1 y−1) • Exogenous C increased the concentration of labile fractions but accumulated mostly in mineral-associated fractions. • Rock-Eval® pyrolysis coupled to PARTY SOC model is more sensitive to the amount of sewage sludge added than other fractionations. • The response of SOC fractions did not directly correspond to that of yield of a cereal-based rotation. Soil organic matter (SOM) is a recognized carbon reservoir and paramount in soil functioning and agrosystems productivity. Different management strategies have been established to enhance SOM in arable soils, and one is the application of exogenous organic matter (EOM). Despite significant efforts in recent years, the consequences of EOM addition on increasing soil organic C (SOC) storage and stability in different pedoclimatic contexts remain incompletely understood. In this study, we evaluated the effect of long-term (28 y) sewage sludge (SS) addition to a calcareous soil supporting rainfed extensive crops in a Mediterranean sub-humid area in terms of SOC stabilization and distribution among functional fractions. To that end, we studied total SOM storage and soil fractions in a long-term experiment comparing 4 different doses of SS with mineral fertilization and no-fertilization controls. We compared the concentration, storage and distribution of C using two different fractionation methods (particulate vs. mineral-associated, defined by granulodensimetric fractionation, and active C vs. stable C defined by Rock-Eval® thermal analysis coupled to the machine learning PARTYsoc v2.0 model) on the tilled layer (0–30 cm). Three soil functioning indicators (crops yield, soil microbial biomass C and aggregate stability) were also quantified. We found that SS application, which slightly increased SOC concentration when SS was added, resulted in a net SOC stock gain only with the highest dose used (80 tons/ha), compared to mineral fertilization, suggesting that most of the C added was mineralized. An uneven response of soil fractions was however detected. The coarsest heavy physical fractions > 250 μm and 50–250 μm in size were the most enriched in their C concentration with SS addition, whereas SOC was mostly accumulated as mineral-associated C in the silt-size (2–50 μm) and the 50–250 μm fractions. Regarding thermal fractionation, SS treatments showed C gains between 57 % and 35 % in the active C pool, compared to mineral fertilization. This can be explained considering that the accumulated SOM in mineral-associated fractions corresponded to mean-residence times in the order of 20–40 years. The consequences on soil functioning indicators were not directly related to the amount of SOC stored in the soil, as the highest SOC gains corresponded to the highest dose, but not the highest yields, and some negative correlations were observed between SOC fractions and soil structural stability and microbial biomass. This can be related to some deleterious effects of excessive SS application reducing yields, the soil biological activity and soil structure, and represents an example of the need to decouple the assessment of soil health from that of SOC storage for certain soil management practices. The overall evaluation of the net consequences of long-term SS application indicated that low doses (10 tons/ha) seem a better choice, as they resulted in the highest efficiency in C incorporation, and in a slightly greater increase in SOC concentration than intermediate doses, and equal yields than mineral fertilization, but did not have the negative effects observed in soil functioning with higher doses. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of biodegradable microplastics (MPs) on abiotic CO 2 varied among soils. • The CO 2 partial pressure controlled the carbonate-derived CO 2 in the short period. • Ammonia-oxidizing bacteria likely drove abiotic CO 2 in the long term. The presence of biodegradable microplastics (MPs) has the potential to affect soil pH, and possibly accelerate or inhibit the loss of soil inorganic carbon (SIC) in calcareous soils. However, most researchers have focused on the release of biotic carbon dioxide (CO 2) from soils following MP amendments, and few studies have investigated SIC-derived CO 2. In this experiment, three typical biodegradable MPs were applied to three calcareous soils amended with 1 % 13C-labeled (99 % atom) carbonate, and the release of CO 2 originating from SIC was quantified. The total CO 2 emissions, soil pH, and microbial functional genes involved in soil nitrification and denitrification were also detected. Throughout the experiment, the contribution of 13C-labeled carbonate to total CO 2 emissions ranged from 0.42 % to 3.31 %. The impact of biodegradable MPs on SIC-derived CO 2 varied with incubation period. At the early stage (≤20 days), the amendment of three biodegradable MPs increased the abiotic CO 2 in some cases, and the CO 2 emissions from 13C-labeled SIC were positively correlated with the total CO 2 originating from the decomposition of SOC and MPs. At the late stage (20–70 days), the presence of biodegradable MPs inhibited the release of CO 2 from 13C-labeled carbonate in most treatments. Moreover, there were negative relationships of SIC-derived CO 2 with soil pH and the amoA gene of ammonia-oxidizing archaea (AOA), but positive correlations of SIC-derived CO 2 with amoA of ammonia oxidizing bacteria (AOB) and nirK and nirS genes encoding nitrate reductase in denitrification. Our results indicate that long-term exposure to biodegradable MPs probably regulates the release of H+ in the nitrification process by controlling AOB, and then controlling the dynamics of SIC in calcareous soils. [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) is sensitive to land use and to physico-chemical soil properties as well soil microbial communities controlling SOM stabilization. Our study aimed at exploring how carbonates of Mediterranean soils – known to stabilize SOM by enhancing soil aggregation and binding SOM by calcium – are affecting SOM and microbial communities under different land uses. In soils with and without carbonates sampled in forests, cultivated and abandoned fields, we have fractionated SOM-pools according to particle sizes and determined C mineralization rates and polyvalent cations in these fractions. In agreement with larger scale assessments in the Mediterranean, our results show that SOM contents are greater in forest than in agricultural soils, but that the differences among land use types depend on carbonate contents. While SOM contents are greater in carbonated soils of forests, cultivated soils have low SOM levels independent of the carbonate content, presumably due to a reduced protection of particulate SOM by century-long intense tillage. Forest soils contain particularly large amounts of SOM associated with the coarser soil fraction. In this fraction, C mineralization was smallest in the carbonated forest soil, possibly due to a low SOM quality indicated by high C/N ratios and low δ15N values. Greater contents of Ca, Fe and Al in carbonated soils also suggests that stabilization through Ca and phyllosilicates was important. Mineralization of sand-associated SOM was highest in cultivated and abandoned soils, which is indicative for a small SOM stabilization, which in turn might restrict SOM accumulation after land abandonment. Microbial communities assessed by phospho-lipid fatty acid signatures and microbial carbon use efficiency were more closely associated with land use than with carbonate content – a pattern that reflects the distribution of C pools among size fractions which differed more strongly among land use types than between soils with and without carbonates. • Land use effects on SOM contents and C mineralization depend on carbonate contents. • Forests have high SOM contents, in particular in carbonated soils. • Soils in cultivated and abandoned land have low SOM levels independent of carbonates. • Land use affects microbial community structure and activity more than carbonates. • C pool distribution and mineralization of size fractions are controlled by land use. [ABSTRACT FROM AUTHOR]

Soil aggregate size and stability are two important factors affecting soil erodibility to wind erosion. In this study, we developed new models to quantify soil erodibility to wind erosion by looking at the mean weighted aggregate diameter (MWD) and the wind erodible fraction (EF) of the soil. These two erodibility indices together with the spectral reflection of soil in the range of Vis– NIR (400–2500 nm) were measured in 511 soil samples. Pedo-transfer functions (PTF) and Spectro-transfer functions (STF) were built using the Multiple Linear Regression (MLR), Partial Least Squares Regression (PLSR), and Support Vector Regression (SVR), considering train(70%) and test (30%) datasets. Result showed that shear strength (SS), organic matter (OM), penetration resistance (PR), and clay content had a significant coefficient (p < 0.05) for predicting MWD and EF indices. Vis– NIR spectroscopy method performed better than PTF method and wavelengths of 513, 773, 872, 1256, 1414, 1488, 1908, 2042, 2210, and 2311 nm were introduced as the key wavelengths for the estimation of soil erodibility indices based on the regression coefficient. Results of the predictive models revealed that SVR outperformed (RMSE = 0.12 mm, RPIQ = 2.56 for MWD; and RMSE = 9.32%, RPIQ = 2.24 for EF) PLSR (RMSE = 0.12 mm, RPIQ = 1.98 for MWD; and RMSE = 9.40%, RPIQ = 1.84 for EF). This study proved that Vis– NIR spectroscopy is a promising method for the prediction of MWD and EF indices as soil erodibility indices. [ABSTRACT FROM AUTHOR]

[Display omitted] • OC was reliably quantified in calcareous POM/MAOM fractions with 4 methods. • Sodium hexametaphosphate (SHMP) dispersion did not affect quantification of OC. • Guidance on the selection of the most optimal OC method is provided. Accurate quantification of soil organic carbon (OC) pools is essential to study the dynamics of OC in soils. Therefore, organic matter is often separated into physical fractions with distinct turnover times, e.g. particulate (POM) and mineral-associated organic matter (MAOM), after which their OC content is measured. Calcareous soils are under-represented in such fractionation studies, because the required analytical differentiation between OC and inorganic carbon (IC) is not straightforward and implies more processing time, sample mass and equipment. Here, we review the performance of four methods to quantify OC in POM and MAOM fractions of soils containing 3–16 g IC kg−1 and 10–25 g OC kg−1 (n = 16). We assessed the similarity and consistency of the data obtained with the different methods. Furthermore, we checked how their ability to distinguish OC from IC was influenced by the fractionation and in particular by the dispersion with sodium hexametaphosphate (SHMP). The four methods were: 1) Elemental carbon analysis after removal of IC by acid fumigation (OC fum); 2) Elemental carbon analysis after removal of IC with aqueous acid (OC aq); 3) Elemental carbon as determined by Rock-Eval 6 thermal analysis (OC RE6); and 4) Elemental carbon analysis after removal of OC by loss on ignition and subsequent quantification of OC by difference between total carbon and IC (OC LOI). We found that the OC fum , OC aq , and OC LOI methods produced similar OC contents for bulk soils, whereas OC RE6 results were slightly but significantly lower. Total recovered OC RE6 contents of the summed POM and MAOM fractions were similar to the bulk soil OC RE6 contents. In contrast, the recovered OC fum , OC aq and OC LOI contents were slightly higher than respective bulk soil OC contents (108–112%), especially in soils with high IC/OC ratios. We show that this was not caused by operational artefacts or chemical changes that occurred during OC fractionation, but rather likely indicated error propagation. We conclude that all 4 methods can reliably quantify OC in POM and MAOM fractions in calcareous soils and that the optimal choice depends on the required accuracy of the results and the available sample mass, lab equipment and processing time. Based on our findings and practical considerations, we provide guidance for the selection of the most optimal OC quantification method to study OC dynamics in calcareous soils. [ABSTRACT FROM AUTHOR]

Abstract Karst ecosystems are vulnerable to degradation and constitute a significant proportion of southwestern China. Here, we explored the amendment of karst soils with biochar in combination with swine manure compost and chemical fertilizer with the aim of improving the microbial community structure and soil nutrient status of these soils. A pot experiment with eight treatments including CK, F, M, MF, B, BF, BM and BMF were set up, where CK was the control, F was chemical fertilizer, M was swine manure compost, and B was wood-derived biochar. The results showed that biochar and biochar-based fertilizer treatments (B, BF, BM and BMF) had higher bacterial diversity (Simpson and Shannon), microbial biomass and soil nutrient content compared to the corresponding no-biochar treatments (CK, F, M, MF), and treatments with compost (M, MF, BM and BMF) had higher values than no-compost treatments (CK, F, B and BF). The cluster and LEfSe analyses showed that different treatments had distinct bacterial community structure and composition; the biochar network (B, BF, BM and BMF) had a higher number of nodes, links and modules than the no-biochar network (CK, F, M and MF), and the compost network (M, MF, BM and BMF) had more complexity than the no-compost network (CK, F, B and BF). Soil variables significantly influenced the biochar and the no-biochar networks, whereas there was no significant correlation with compost or no-compost networks. In conclusion, additions of both biochar and organic compost induced microbial correlation network complexity increases and improved the soil nutrients, indicating biochar-based fertilizer had great benefits on restoration of karst degraded soil. Highlights • Biochar-based fertilizer induced bacterial community structure and composition shifts and increased microbial correlation complexity. • Biochar-based fertilizer significantly increased soil nutrients content. [ABSTRACT FROM AUTHOR]

Abstract It is widely believed that soil disturbance by tillage was the primary cause of historical soil organic carbon (SOC) loss and high carbon dioxide (CO 2) emission levels in the calcareous karst region. Nevertheless, the mechanisms underlying CO 2 fluxes resulting from the soil property changes caused by tillage are poorly understood. A one-year simulation experiment using different tillage frequencies was conducted to quantify the impacts of tillage and soil property changes on CO 2 flux. Treatments included conservation tillage (T0), semiannual tillage (T1), tillage every four months (T2), bimonthly tillage (T3), and monthly tillage (T4). The effects of tillage on soil CO 2 flux had a strong seasonal pattern. CO 2 fluxes in higher tillage frequencies of T3 and T4 were significantly higher than those of other treatments in spring, summer, and autumn. For viable tillage management, CO 2 fluxes in T1 and T2 were significantly higher than those in T0 in spring and autumn. No significant differences in CO 2 flux were found among treatments in winter. Tillage also had a significant influence on soil biogeochemical properties. Aggregate stability, dissolved organic carbon (DOC), and microbial biomass carbon (MBC) significantly decreased in T2, T3, and T4, whereas SOC significantly decreased just in T3 and T4 after 1 year. A structural equation model analysis showed that the annual cumulative soil CO 2 flux was directly affected by annual changes in SOC (∆SOC), DOC (∆DOC), and MBC (∆MBC). Tillage frequency directly influenced annual changes in large macroaggregates (∆AG) and ∆MBC. These results indicated that tillage practice indirectly lowered SOC by reducing large macroaggregates and microbial biomass, which in turn, enhanced CO 2 flux. Our results suggested that tillage disturbance in the karst soil significantly increased SOC loss through enhanced CO 2 flux compared with that in the non-karst soil in a similar climate. In contrast, reducing or eliminating tillage in the wet-hot season could lower CO 2 flux rate by minimizing large macroaggregate disturbance and, by extension, microbial access to mobile carbon sources. Graphical abstract Unlabelled Image Highlights • Karst soil was sensitive to tillage, and traditional tillage increased CO 2 fluxes. • Frequent tillage decreased aggregate stability, SOC, DOC, and MBC after 1 year. • Reduced tillage frequency in the wet-hot season was decreased CO 2 fluxes. • CO 2 fluxes were affected by tillage through decreased large macroaggregates, MBC, and SOC. [ABSTRACT FROM AUTHOR]

Ammonia-oxidizing bacteria-driven autotrophic nitrification dominated nitrous oxide production in calcareous soil under long term plastic film mulching. [Display omitted] • Ammonia-oxidizing bacteria (AOB) and autotrophic nitrification dominated N 2 O production in calcareous soil. • Long-term film mulching decreased the abundances of key N 2 O production gene abundances. • Film mulching decreased autotrophic nitrification and AOB derived N 2 O production. • N fertilization increased autotrophic nitrification and the relative contribution of AOB. Fertilized cropland soils are a major source of anthropogenic N 2 O emissions in terrestrial ecosystems. However, the main N 2 O production pathways and microbes underlying N 2 O production in calcareous cropland soil under long-term plastic film mulching and nitrogen (N) management have not yet been clarified. Here, we used 15N tracing combined with quantitative polymerase chain reaction to evaluate the relative contributions of different N 2 O production pathways (i.e., autotrophic nitrification, heterotrophic nitrification, and denitrification) to N 2 O production in a calcareous maize field soil; we also used specific inhibitors (acetylene and 1-octyne) to determine the functional importance of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to N 2 O production. Autotrophic nitrification accounted for 47–63% and 76–100% of total N 2 O emissions in unfertilized (F 0) and N-fertilized soils, respectively. AOB accounted for 62% and 91–98% of total N 2 O production in F 0 and N-fertilized soils, respectively. N 2 O production was significantly lower in soils following long-term film mulching (F 225) compared with the bare land soil (N 225), and this was due to the reduced abundance and activity of AOB and N 2 O derived from autotrophic nitrification. Autotrophic nitrification-derived N 2 O emissions were 2.2-fold, 3.6-fold, and 6.3-fold higher in the F 225 treatment (appropriate N level), the treatment in which the level of N was the same as that applied by local farmers (F 380), and the manure addition treatment (F 225+M) compared with F 0 , respectively, indicating that autotrophic nitrification was the main driver of increases in N 2 O emissions. These findings provide the first direct evidence showing that AOB-driven autotrophic nitrification is the dominant N 2 O production pathway in the plastic film mulched calcareous soils under different agricultural management practices. Our results also show that autotrophic nitrification is depressed by long-term mulching and promoted by N fertilization. These findings have implications for the development of targeted N 2 O mitigation strategies. [ABSTRACT FROM AUTHOR]

• Sodicity was investigated in a semiarid Calcisol of the Great Konya Basin. • pH gradually increased while the EC decreased with irrigation water treatment. • Water quality strongly influenced ion concentrations in calcareous soils. • Short-term leaching with poor-quality waters restricts permeability. • Poor quality irrigation treatments increase the risk of secondary salinization. The often-indispensable use of poor-quality irrigation water in drylands instigates diverse physicochemical dynamics leading to soil salinization and sodicity which are recognized as major contributors to land degradation. This study aimed to examine the effects of water quality and irrigation mode on solute transport conditions in terms of ion exchange of colloidal particles. Laboratory studies with undisturbed soil columns were carried out with two water treatments - tap and sodic waters - as well as two water flow velocities: fast leaching which corresponds to Darcy velocity equal to the saturated hydraulic conductivity and slow leaching equal to half the fast-leaching case. Results indicated that the flow velocities did not significantly influence pH, EC and ion concentrations due to the high calcium carbonate and clay contents of the soil which make the soil less permeable. However, flow velocity rapidly decreased in the fast leaching compared to that in slow leaching as the sodic water was applied. This reveals the destructive effect of Na+ in the soil. The EC rapidly dropped at the beginning of leaching for both water qualities opposite to pH, then became steady. All sodic applications caused an increase in Na+ till the end of treatments. This also resulted in variations in measured soluble anions. In general, sharp decreases in highly soluble anions were observed in all treatments, leading to an increase in HCO 3 –, especially for sodic treatments. Overall, sodicity caused significant changes in flow dynamics and ion concentrations and created favorable conditions for secondary salinization in this low permeable soil system. [ABSTRACT FROM AUTHOR]

Management of phosphorus (P) loss in soils with heavy manure application requires improved understanding of the transformation characteristics of soil P. Influences of manure application on the forms and sorption-desorption characteristics of P in surface (0–30 cm) and subsurface (30–60 cm) layer of a calcareous soil were investigated in a six-year field trial in comparison to chemical fertilizer application. Hedley fractionation and P K-edge X-ray absorption near-edge structure spectroscopy were used to determine the soil P forms. Manure (M) and chemical fertilizer (F) treatments resulted in P accumulation in two soil depths, but the total P accumulation in surface soil with M treatment was significantly lower than F treatment with similar P surplus. Compared to control, M and F treatments were significantly increased the proportion of labile P at both depths. In surface soil, M treatment significantly decreased stable Ca-associated P proportion and increased Fe-associated P and inositol hexakisphosphate proportions. The accumulation and transformation of P in M treatment distinctly decreased P sorption maximun, sorption coefficient and buffer capacity, and increased the degree of P saturation and P desorption relative to F treatment. The soil properties of pH, organic carbon (OC), total nitrogen (TN), Mehlich-3 extractable Ca and Fe, and phytase in surface soil and pH, OC, TN, Mehlich-3 extractable Ca and dehydrogenase in subsurface soil had significant effects on the compositions of soil P ( P  < 0.05), respectively. Lowered pH due to manure application mainly contributed to P transformation and release in the calcareous soil. [ABSTRACT FROM AUTHOR]

Growing production of manufactured nanomaterials has increased the possibility of contamination of groundwater resources and soils by nanoparticles (NPs). It is crucial to study the fate of NPs in subsurface porous media in order to evaluate and control their risks to ecosystems and human health. Hence, this study was conducted to investigate the transport and retention of polyvinylpyrrolidone (PVP) stabilized silver nanoparticles (AgNPs, a diameter of 40 nm) under saturated and unsaturated conditions in intact columns of two calcareous sandy loam (TR) and loam (ZR) soils. Furthermore, similar experiments were conducted using sand quartz as a reference medium. A pulse of the AgNP suspension with an input concentration ( C 0 ) of 50 mg L −1 was injected into the columns for 3 pore volumes. The transport of bromide (Br), as a non-reactive inert tracer, was also examined. High mobility of AgNPs was observed through the sand columns due to unfavorable conditions for AgNP deposition on the quartz sand surfaces. Nearly all AgNPs introduced into the columns of both soils were retained in the soil. Percentages of AgNPs leached out of the columns were <1% of the total injected mass in both soils. Hyperexponential retention profiles (RPs) were observed in both soils and maximum concentrations of 100–130 mg kg −1 were determined near the columns' inlet. However, slightly stronger retention of AgNPs and greater maximum retained concentrations on the solid phase ( S max ) in the ZR soil compared with the TR soil may be attributed to smaller grain sizes of the ZR soil. Hydrodynamic forces adjacent to the solid surfaces near the column inlet can provide a viable explanation for the hyperexponential shape of RPs. The one-site kinetic attachment model in HYDRUS-1D, which accounted for time- and depth-dependent retention, was successfully used to analyze the retention of AgNPs. The results showed that the degree of saturation had little effect on the mobility of AgNPs through undisturbed soil columns. Our results suggested the limited transport of AgNPs in neutral/alkaline calcareous soils under both saturated and unsaturated conditions. [ABSTRACT FROM AUTHOR]

Soil Visible–Near-Infrared (Vis-NIR) spectroscopy has become an applicable and interesting technique to evaluate a number of soil properties because it is a fast, cost-effective, and non-invasive measurement technique. The main objective of the study to predict soil erodibility (K-factor), soil organic matter (SOM), and calcium carbonate equivalent (CaCO 3 ) in calcareous soils of semi-arid regions located in south of Iran using spectral reflectance information in the Vis-NIR range. The K-factor was measured in 40 erosion plots under natural rainfall and the spectral reflectance of soil samples were analyzed in the laboratory. Various soil properties including the CaCO 3 , soil particle size distribution, SOM, permeability, and wet-aggregate stability were measured. Partial least-squares regression (PLSR) and stepwise multiple linear regression (SMLR) were used to obtain effective bands and develop Spectrotransfer Function (STF) using spectral reflectance information and Pedotransfer Function (PTF) to predict the K-factor, respectively. The derived STF was compared with developed PTF using measurable soil properties by Ostovari et al. (2016) and the Universal Soil Loss Equation (USLE) predictions of the K-factor. The results revealed that the USLE over-predicts (0.030 t h MJ − 1 mm − 1 ) the K-factor when compared to the ground-truth measurements (0.015 t h MJ − 1 ) in the semi-arid region of Iran. Results showed that developed PTF had the highest performance (R 2 = 0.74, RMSE = 0.004 and ME = − 0.003 t h MJ − 1 mm − 1 ) to predict K-factor. The results also showed that the PLSR method predicted SOM with R 2 values of 0.67 and 0.65 and CaCO 3 with R 2 values of 0.51 and 0.71 for calibration and validation datasets, respectively. We found good predictions for K-factor with R 2 = 0.56 and ratio of predicted deviation (RPD) = 1.5 using the PLSR model. The derived STF (R 2 = 0.64, RMSE = 0.002 and ME = 0.001 thMJ − 1 mm − 1 ) performed better than the USLE (R 2 = 0.06, RMSE = 0.0171 and ME = 0.0151 thMJ − 1 mm − 1 ) for estimating the K-factor. [ABSTRACT FROM AUTHOR]

Zinc (Zn) deficiency is a widespread problem in wheat-cultivated lands, and understanding important mechanisms determining Zn phytoavailability is of high importance. Accordingly, a two-year field experiment was conducted to investigate the effects of two Zn-deficiency tolerant wheat cultivars on Zn binding forms in a calcareous saline soil. Changes in soil Zn fractions were also found to be related to Zn uptake by wheat. Rhizosphere and bulk soil samples and the above-ground biomass were collected at grain maturity and analyzed for Zn. By using a sequential extraction procedure, soil Zn was divided into the following operationally defined fractions which are conceptually designated: ‘exchangeable Zn’ (EXCH-Zn), ‘Zn bound to carbonates’ (CAR-Zn), ‘organically bound Zn’ (ORG-Zn), ‘Zn bound to iron and manganese oxides’ (FeMnOX-Zn), and ‘residual Zn’ (RES-Zn). EXCH-Zn and ORG-Zn in the rhizosphere soil were found to be positively correlated with Zn uptake into the aboveground biomass of both wheat cultivars, thereby indicating that these fractions could be considered as labile pools. Higher EXCH-Zn and ORG-Zn fractions were determined in the rhizosphere, not in the bulk soil, whereas the non-labile Zn pools was decreased, suggesting strong Zn solubilization due to the input of acidity and organic compounds by root and the associated microbial activity. The differences between rhizosphere and bulk soil in EXCH-Zn and ORG-Zn were associated with the lower pH and the higher concentrations of the total (TOC) and dissolved organic carbon (DOC) in the rhizosphere. The fact, these effects (lower pH and higher DOC in the rhizosphere, rather than in the bulk soil) were stronger for Back Cross Rushan than were for Kavir; this was in line with the higher Zn uptake of Zn-deficiency tolerant Back Cross Rushan. [ABSTRACT FROM AUTHOR]

Application of pyrolysed feedstocks or biochar has the potential to affect soil enzyme activity and function. Nevertheless, our detailed understanding of the mechanisms responsible for biochar-enzyme interaction is limited in arid soils. The main aim of this study was to study how the potential activity of several extra- and intra-cellular enzymes involved in C and N cycling, and microbial metabolism would respond to addition of biochar in two calcareous soils with fine and coarse texture. Three corn stalk biochars were prepared at 200, 400 and 600 °C and added to sandy and clayey soils at 0.5 and 1% (w/w). Soils with uncharred feedstocks; and without biochar and feedstock additions as the control treatment were also included in the experiment. The potential activities of soil enzymes were assayed. Compared with the control, addition of uncharred and charred feedstocks significantly stimulated the activities of catalase (1.3- to 4.3-fold), dehydrogenase (1.2- to 3.1-fold), cellulase (1.1- to 1.7-fold), invertase (1.3- to 5.8-fold) and protease (1.03- to 2.9-fold), which varied with pyrolysis temperature and addition rate as well as soil texture. The positive effects of biochar addition on soil enzymes were much greater at 1% than 0.5% application rates for all the assayed enzymes and in sandy than clayey soils for catalase, dehydrogenase and invertase. The change in enzyme activity with biochar addition primarily attributed to the change in soil microbial biomass. However, enzyme activities were lower in the soils amended with charred than uncharred biomass, and decreased as pyrolysis temperature increased. Our results showed clearly that uncharred feedstock and lower temperature biochars gave higher benefits to both contrasting textured soils than higher temperature biochars, largely connected to changes in the physiochemical properties of biochars. Nevertheless; long-term field experiments are required to verify whether the beneficial effect of uncharred vs. charred feedstocks would be maintained over long timescales under the conditions of this study. We conclude that although biochar application may improve enzyme activities of calcareous soils with low organic matter content, increasing pyrolysis temperature adversely affects soil enzymatic functions, depending mainly on soil texture and application rate. The study evidently indicates that corn biochar addition to arid-soils may have a high potential for improving the enzyme activities as important indicators of soil quality, and subsequently carbon sequestration and biogeochemical cycles. [ABSTRACT FROM AUTHOR]

Acidification of cropland soils is a serious problem in China that may cause long term pH decline, which threatens the sustainability of soil fertility and crop yields. The objective of this research was to investigate those rates and mechanisms for a slightly calcareous soil. The field data were based on selected treatments from a long-term (1991–2015) N fertilization experiment at a rice-wheat rotation on a slightly calcareous (pH 7.7), young and hardly weathered clay soil (Regosol), including two plots with urea and NH 4 Cl fertilization and a control plot (no N fertilization). Urea and NH 4 Cl were applied at annual rates of 300 kg (1991–1996) and 285 kg (1997–2015) N ha − 1 . Soil pH and exchangeable Ca 2 + and Mg 2 + declined in the first 12 years for the urea treatments, but remained constant thereafter. For the NH 4 Cl and control treatment, the exchangeable base cations showed an oscillating decrease over the 25 years. Soil pH and exchangeable Ca 2 + , and Mg 2 + levels were significantly ( P < 0.05) lower in the NH 4 Cl treatment plot than the control. After 25 years, soil pH in the plots receiving urea and NH 4 Cl were 0.9 and 2.0 units lower than the control, respectively, while the total exchangeable base cations were about 10% and 16% lower, respectively. Carbonate dissolution, base cation exchange and mineral weathering were the main H + buffer pathways of the Regosol. Long-term N fertilization favored the formation of smectite and vermiculite and accelerated the weathering of mica, potassium feldspar, and illite. This was more evident in the NH 4 Cl treatment than in the urea treatment. Consequently, the soil acid-buffering capacity was slightly enhanced after year 13 in the order of urea > control > NH 4 Cl. The increased weathering of soil primary minerals and clay minerals was the main reason that soil pH and exchangeable base cations stayed constant after about 12 years. [ABSTRACT FROM AUTHOR]

The present study investigated kinetics of phosphorus (P) release from some calcareous soils employing DGT technique. For these purpose, DGT were deployed in ten calcareous soils for different time periods between 4 h and 21 days and the accumulated P were used to calculate the distribution coefficient for labile metal, K dl , desorption rate constants (k − 1 ) and the rate at which the soil system can resupply P from solid phase to solution (Tc) using the DIFS model. The values of K dl calculated from DIFS ranged from 0.67 to 198 cm 3 /g. Response times (Tc) were so short in six studied soils with low Olsen-P. A short response time means that the rapid resupply from the solid phase and slow depletion over time of the available P pool occurs. By contrast, the four rests of the soils have a longer response time (about 40 min) and so little the resupply from the solid phase, leading to a progressive depletion. The P desorption rate (k − 1 ) parameter derived from DIFS were from 9.9 ∗ 10 − 6 to 21.12 ∗ 10 − 4 s − 1 with a mean 4.54 ∗ 10 − 4 and well-correlated with the content and/or the concentration of P in corn shoot (r = 0.74, P < 0.05) and root (r = 0.71, P < 0.05) confirming the importance of P desorption rate in plant P nutrition in the calcareous soils. In these study, the close correlation was obtained between clay and calcium carbonate equivalent concentration with P desorption rate that demonstrate DGT technique sensitive to soil properties and may allow the study of root-induced changes in rhizosphere. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) level is influenced by incorporation of crop straw and application of nitrogen (N) fertilizer, which are typical farming practices in intensive agricultural regions. However, the interaction between the N fertilization and crop straw incorporation on SOC levels is still not univocally established, especially for calcareous soils. We therefore conducted a 224-day laboratory incubation experiment with four levels of 13 C-labeled maize straw amendment (0, 1 ×, 3 × and 5 × of maize straw yield) and three N fertilization rates (0, 300, and 600 kg N ha − 1 a − 1 ) on a Fluvic Cambisol to investigate the short-term response of SOC content. The 13 C-labeled straw allowed partitioning of the CO 2 produced from native SOC or crop straw for application to a two-compartment exponential decay model to simulate the addition of new SOC from the straw and the decomposition of the native SOC. The addition of maize straw caused immobilization of inorganic N during the incubation. Increased mineral N fertilization significantly inhibited the decomposition of maize straw, which led to the increased new SOC from maize straw amendment. Priming effect (PE) of native SOC decomposition peaked at 40 days after incubation, and then decreased until the end of the incubation. N fertilization significantly enhanced the cumulative PE when maize straw was not added (N2 induced PE at C0 was + 19% of C0N0 SOC decomposition), but had no significant effect when the highest rate maize straw was amended (N2 induced PE at C5 was 8% of C0N0 SOC decomposition), indicating that maize straw amendment can moderate the PE promoted by N fertilization. There was a positive linear correlation between the cumulative PE and the input of maize straw C. An increase in maize straw incorporation with N fertilization caused the largest increase in total SOC content at the end of 224-day incubation (the highest 23.7% for C5N2 treatment, i.e., 5 × maize straw yield + 600 kg N ha − 1 a − 1 ). Our findings highlight that in intensively managed agricultural regions, integrating N fertilization with crop residue amendment can promote SOC sequestration and the retention of fertilizer N in the soil. The results are particularly relevant for developing new or improved farming methods in areas with calcareous soils, such as northern China. [ABSTRACT FROM AUTHOR]

The properties of and processes in calcareous soils are important in the context of dryland soil management and moderation of atmospheric CO 2 by carbonate weathering. This study was conducted to determine the major and trace elemental composition in soils of the Kurdistan region of Iraq, and their geochemical features. Soil samples were taken from seven pedons, five of them from forest soils and two others from non-cultivated soils. Selected physical properties, total concentrations of elements and mineralogical properties were determined on samples from each horizon. Weathering processes in the soils are characterised by loss of Ca, Sr and several trace elements, and accumulation of less mobile elements such as Zr, Ti, and Al. The progress of carbonate weathering was best expressed using Ba/Sr and Rb/Sr ratios. Principal components analysis confirmed that distinctive geochemical differences for two profiles (significantly higher Mg, Co, Cr, Mn, and Ni) were likely to represent control by parent material, a conclusion reinforced by both mineralogical differences and the location of profiles relative to surficial geology. The other main geochemical processes differentiating the pedons were chemical weathering of carbonates and accumulation of residual elements. Calculation of absolute mass flux ( τ ) values showed that, for some profiles, concentration of mobile elements such as Na and K by evapotranspiration was potentially important, despite evidence for clay eluviation in most profiles. Absolute loss of several elements was also correlated with increased weathering as measured by Ba/Sr ratios. None of the forest soils showed enrichment-depletion ( τ ) profiles for Fe or Al consistent with podzolisation. This study highlights useful geochemical approaches to understanding chemical weathering and pedogenesis in calcareous soil profiles. [ABSTRACT FROM AUTHOR]

The extensive use of silver nanoparticles (AgNPs) in consumer and medical products leads inevitably to release of such particles into environment and soil resources. This study was conducted to provide evidences for biological effects of AgNPs in two calcareous soils with different textures and salinity levels. Basal respiration (BR) and substrate-induced respiration (SIR), as indicators of soil microbial activity and biomass, respectively, were determined in the calcareous soils spiked with a dilution series of AgNPs and AgNO 3 . Urease and alkaline phosphatase activities were also measured in the spiked and control soils. Finally, dose–response approach was used to model the sensitivity of the soil biological properties to AgNPs and AgNO 3 contamination. The results revealed that the effects of AgNPs and AgNO 3 on the soil respiration and enzyme activities depended on Ag dose and soil type. For instance, soil respiration was not affected or even stimulated by low doses of AgNPs and AgNO 3 , but negatively affected by high doses (> 20 mg Ag kg − 1 ). Soil urease and phosphatase activities were generally inhibited in the presence of AgNPs and AgNO 3 , though in low Ag concentrations there was no inhibition or even stimulation. Generally, the ecological dose (ED) values of AgNPs were smaller than those of AgNO 3 , suggesting that AgNPs have more negative effects than AgNO 3 on the soil microbial and enzyme activities, at the same level of Ag dose. The results also revealed that suppression of microbial and enzyme activities by AgNPs and Ag ions are greater in the soil with lower clay content and ionic strength. [ABSTRACT FROM AUTHOR]

Aerobic soils are generally known as potent sinks for the atmospheric greenhouse gas methane (CH 4 ). However, uptake rates vary greatly depending on the soil site, and hence estimation of the global soil sink is difficult. Here, we measured the in situ CH 4 flux of 15 forests and 14 grasslands on siliceous or calcareous parent materials in summer 2013. To cover the topography of North Tyrol (Austria), sampling sites were distributed over four typical altitudes (500, 1000, 1500, and 2000 m above sea level). Twenty-three of the soils were net sinks for CH 4 , whereas net CH 4 emission occurred at four grassland sites and two sites neither showed net removal nor emission. Flux rates ranged between − 3.2 and 2218.2 μg CH 4 -C m − 2 h − 1 for grasslands, and between − 3.2 and − 45.0 μg CH 4 -C m − 2 h − 1 for forests, thus showing that forest soils are significantly more efficient sinks than grassland soils. Soils derived from siliceous parent material were significantly more effective sinks than those derived from calcareous parent material, when only negative flux rates were considered. Multiple regressions indicated that soil dry mass and NH 4 + -N shaped CH 4 flux of grasslands, whereas CH 4 flux of forest soils was regulated by soil pH and NO 3 − -N. Our results provide insights into the CH 4 turnover of the so far scarcely studied Central European alpine regions and thus add to the knowledge on this relevant topic. [ABSTRACT FROM AUTHOR]

The forms of phosphorus (P) in animal manure composts are different from that of synthetic P fertilizers, and this affects how soil P chemistry will be altered when they are used as P amendments. This study is an extension of a previously reported incubation study, where the net changes in the nature and dynamics of plant available P forms applied either as inorganic P (KH 2 PO 4 ) or turkey litter compost (TLC) without plant growth were analyzed. The objective of this study was to analyze the net changes in the nature and dynamics of plant available P forms with plant growth in the greenhouse. The amounts of various P forms dependent on their solubility in soils were measured by a sequential fractionation method after 4, 8, 12 and 16 weeks incubation. The majority of TLC-P (brushite and newberyite) was recovered in the moderately labile P extracted with a weak acid. Though the labile P fraction in the TLC-treated soil was smaller than that in the fertilizer-treated soils, ryegrass growth was greater. Net transformation/plant uptake of the labile/moderately labile P was faster in the TLC-treated soil than the fertilizer-treated soil. A weak acid extractable inorganic P fraction should be considered as plant available P, especially in the compost-treated soil, which would be converted into plant available P through direct and/or indirect root-induced acidification in the rhizosphere. [ABSTRACT FROM AUTHOR]

This study was conducted to derive the relationships of soil shrinkage parameters and indices with soil and environmental variables in calcareous soils. Ninety nine undisturbed clods were collected from surface soils in hilly regions of Cherlgerd, western Iran. Soil shrinkage curve was measured based on Archimedes ' principle, by covering the clods with an acrylic resin. The shrinkage curve data were modeled using Peng and Horn (2005) model. The model's fitting parameters and several shrinkage indices (i.e. relative void ratio changes, mean slopes at various shrinkage zones, coefficient of linear extensibility, and total and relative shrinkage capacities) were predicted using multiple linear regression models by including soil properties (pedotransfer functions, PTFs) and by combination of soil properties and environmental variables (soil spatial prediction functions, SSPFs) as inputs. The results showed that, on average, the structural, proportional, residual and zero shrinkage zones comprised 17.2, 66.2, 15.2 and 1.4% of total shrinkage for the studied soils. The shrinkage capacity (ShC) and relative shrinkage capacity (Δ e total-rel ) varied, respectively, in the ranges 0.204–0.641 and 0.288–0.589 in the studied soils. While clay fraction increased the ShC and Δ e total-rel , organic matter had a diminishing effect on the Δ e total-rel . An extended structural zone was observed in fine-textured soils, presumably due to greater aggregation. Volume change in the structural shrinkage zone was greater in weakly-structured calcareous soils because carbonates would minimize resistance of aggregates against the shrinkage forces. PTFs could explain 12–48% of variability of the model's parameters, and the inclusion of topographic attributes (i.e. SSPFs) significantly increased R 2 values. Developed PTFs could explain 11–41% of variability of the shrinkage indices. The particle size fractions and relative bulk density were identified as most important soil properties for the prediction of shrinkage indices. Overall, the use of SSPFs by including topographic attributes such as dispersal area, elevation, surface curvature and plan curvature and normalized difference vegetation index (NDVI) could improve the performance of the prediction functions for soil shrinkage indices. [ABSTRACT FROM AUTHOR]

• Vis-NIR spectra showed good potential to predict soil properties by PLSR and STFs. • STFs accurately predicted sand, clay and CCE (0.78 ≤ R2 val ≤ 0.83) • STFs predicted pH, K, Mg, Fe, Mn, Cu and Zn with good accuracy (0.65 ≤ R2 val ≤ 0.71) • STFs predicted silt, EC, Na and Ca with acceptable accuracy (0.55 ≤ R2 val ≤ 0.63) • STFs are highly recommended to predict sand, clay, CCE, pH, K, Mg, Fe, Mn, Cu and Zn. Spectroscopy in visible (Vis) and near-infrared (NIR) provides a rapid, timely, non-destructive, low-preparation, and less expensive analysis of soil samples in comparison with traditional laboratory analysis. Therefore, the objectives of this study were to predict basic physical and chemical properties of calcareous soils using Vis-NIR spectral reflectance data by applying partial least square regression (PLSR) and stepwise multiple linear regression (SMLR) approaches and finally to develop spectrotransfer functions (STFs). The target soil properties including sand, silt, clay, pH, electrical conductivity (EC), calcium carbonate equivalent (CCE), and water-soluble sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg), in 234 soil samples, and DTPA-extractable iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn), in 161 soil samples, were measured using standard laboratory procedures in calcareous soils of Fars province, Iran. The spectra of soil samples in Vis-NIR region (400–2500 nm) were collected using Rapid Content Analyzer spectrophotometer (NIRS XDS model) apparatus. Results revealed the better performance of developed PLSR models compared to STFs to predict most of the target soil properties; however, their capability differences were not significant. The STFs predicted sand, clay, and CCE with very good accuracy (0.78 ≤ determination coefficient of validation dataset, R2 val ≤ 0.83); pH, K, Mg, Fe, Mn, Cu, and Zn with good accuracy (0.65 ≤ R2 val ≤ 0.71); and silt, EC, Na, and Ca with acceptable accuracy (0.55 ≤ R2 val ≤ 0.63). It is strongly recommended to use the related STFs for predicting sand, clay, CCE, pH, K, Mg, Fe, Mn, Cu, and Zn of calcareous soils in order to save time and costs, less use of chemicals, and mapping large areas. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pedogenesis in terrace soils begins chaotically. • Terrace soil pedogenesis partly disaccords with classical soil models. • Early stages of terrace soil pedogenesis begin at a different starting point than the original natural soil. • At 'time zero', terrace soils already bear mature constituents. • Terrace soils should be included in soil classification and soil mapping. Agricultural terraces are the most widespread archaeological landforms worldwide. Despite their far-reaching prevalence in many inhabited parts of the world, archaeological soils in terraces (hereafter 'terrace soils') are scarcely studied and their nature is poorly defined. This study aims to depict a space–time framework for the development of calcareous soils in archaeological stone-wall bench terraces and suggest modifications to their soil classification and mapping. To do so, we examined soils at the forefront of five terraces in Catalonia (Spain), that had been previously dated with optically stimulated luminescence to periods from Medieval-Late Middle Ages (1200 ± 60 CE) to Modern (1810 ± 15 CE). Local soils surrounding the terraces are Entisols and Inceptisols in the relatively drier areas and Mollisols in the moister areas. Methods applied are field survey, standard physico-chemical analyses, and soil micromorphology. CaCO 3 content, P, OM and CEC show irregularly trending values throughout the profiles. Micromorphology shows abundant content of charred components throughout the profiles and slight discontinuous carbonate recrystallization, mostly biogenic. Based on these observations, the main parent material was determined to be local soil that was redeposited by workforce as fill material for terracing. We further interpret that pedogenesis mainly involved structure development under the influence of anthroturbation and bioturbation, inheritance of ex situ aggregates from parent soil, reaggregation with little occurrence of organic matter, and low levels of lessivage and CaCO 3 redistribution. We found that pedogenesis in these terraces started in a chaotic manner, considerably faster than pedogenesis in natural soils, primarily influenced by the act of terracing, the maturity of its inherited parent soil material, and relatively large depth. Therefore, early stages of terrace soil development can differ greatly from known soil models, questioning paradigms of pedogenic 'time zero' and 'maturity' in terrace soil. We suggest four terrace fill settings for terrace material and propose a model for the state of entropy and development of terrace soils. We classify the studied soils as Archaeo-Anthroportic Xerorthents, (Anthrosols (Calcaric, Escalic)), and Archaeo-Anthroportic Typic Haploxerolls (Anthrosols (Calcaric, Escalic, Relocatic, Anthromollic)), both overlying buried Inceptisols (Cambisols). Our primary conclusion is that terrace soils should be separately classified and mapped by treating terracescapes as distinct morpho-stratigraphic units in which age is the same as the age of their geomorphic surface. This study advances the pedological understanding of archaeological stone-wall bench terraces and identifies gaps in the understanding of terrace soils. [ABSTRACT FROM AUTHOR]

The variations in soil N cycling after slash-and-burn practice. [Display omitted] • A 15N tracing study was employed to quantify the soil N cycling in the karst area. • Soil gross N transformation rates decrease significantly half-year post-fire. • Slash-and-burn lowers the inorganic N supply capacity in calcareous soils. • Declined soil organic carbon is one of the main causes of the altered N turnover. • Soil microbial community structure rather than population size impacts N turnover. Slash-and-burn is a common practice in the subtropical karst areas of southwest China, as well as in other places around the world, to prepare forest land for agricultural plantations. Understanding the effect of slash-and-burn practice on soil nitrogen (N) supply capacity is critical for the preservation of ecosystem services including long-term plant productivity. This is of particular relevance in mountainous karst regions with thin calcareous soils characterized by high pH, high calcium (Ca), and high soil loss risk. In this study, a 15N tracing approach was employed to quantify the effect of slash-and-burn on gross N -transformation rates and the mineralization-immobilization turnover (MIT) in soils from subtropical karst regions half-year after the burning, right before the agricultural cultivation began. Soil samples were collected from burned and nearby control sites (woodland). Compared to the control sites, the contents of soil organic carbon, total N, and Ca were lower in the burned sites, while no significant difference was observed in soil enzyme activities. The rates of mineralization of organic N to ammonium (NH 4 +), NH 4 + adsorption and release, NH 4 + oxidation to nitrate (NO 3 –) (i.e., autotrophic nitrification, O NH4), and microbial NO 3 – immobilization were significantly lower in burned sites, suggesting that slash-and-burn has a negative effect on MIT in karst regions. The mean residence times of inorganic N were 4.33 ± 0.53 d-1 for NH 4 + and 6.83 ± 1.76 d-1 for NO 3 – in burned soil, which is remarkably higher than the control soil (0.77 ± 0.08 d-1 for NH 4 + and 2.47 ± 0.83 d-1 for NO 3 –), indicating decreased N turnover after slash-and-burn. Abundances of bacteria and fungi, reflected by 16 s rRNA and ITS gene analyses, were not different between burned and control sites, suggesting that microbial community composition and activity, rather than the population size, controls the microbial-modulated N transformations. Owning to the slower NH 4 + and NO 3 – turnover and reduced soil N transformation rates, we conclude slash-and-burn practice significantly lowers soil inorganic N supply capacity, leading to remarkably reduced soil inorganic N content, especially for NO 3 – (from 59.9 ± 8.67 mg N kg−1 to 44.1 ± 1.86 mg N kg−1), which may further restrict the efficiency of agricultural exploitation. Thus, we recommend that the follow-up agricultural activities after slash-and-burn practice need to take this into account in addition to erosion control and nutrient conservation measures. [ABSTRACT FROM AUTHOR]

• Total soil heavy metal contents near old Zn smelters are higher than further away. • HNO 3 -extractable heavy metal pool consistently larger than DTPA-extractable pool. • Reactive soil organic matter fraction lower in soils nearby old Zn smelters. • Using HNO 3 -extractable metals in MSM overpredicts solubility in calcareous soils. • DTPA is recommended for assessing the reactive metal pool in calcareous soils. Multi-surface modelling (MSM) is an important tool to predict heavy metal partitioning and speciation in soils. However, calcareous clay soils contaminated by smelting activities and mine waste have so far received little attention in MSM studies. In this work, 6 paired soil samples taken nearby former Zn smelters and at further distance were used for quantifying the essential input parameters for MSM including the size of the geochemically reactive pool of heavy metals and the reactivity of soil organic matter (SOM) for metal binding. The reactive heavy metal pool (Cd, Cu, Ni, Pb, and Zn) in these samples was determined by extracting soil with 0.43 M HNO 3 and 0.005 M DTPA. For both extraction methods, the contribution of all heavy metals to their total contents was larger in most of the soil samples taken nearby former Zn smelters than in the paired samples from further distance. Furthermore, the amounts of heavy metals extracted with 0.43 M HNO 3 were consistently larger than those extracted with 0.005 M DTPA. The sum of the humic acid (HA), fulvic acid (FA) + hydrophobic organic neutral (HON) fraction varied between 6.2 and 43% of total SOM with an average of 24%, which is at the lower end of what is commonly reported in literature. The lower SOM reactivity might be attributed to a lower humification rate of fresh soil organic matter due to heavy metal contamination. The accuracy of the MSM-predicted predictions of solubility of the heavy metals, especially for Ni and Zn, was higher when the results of the DTPA extraction method were used as model input, than when using the results of the HNO 3 extraction method, especially when the soil carbonate content was > 4%. Hence, the measurement of the geochemical reactivity of heavy metals by the 0.005 M DTPA extraction method and the reactivity of SOM enable adequate MSM predictions of the solubility of heavy metals in smelter slag-contaminated calcareous clay soils. [ABSTRACT FROM AUTHOR]

• The calcareous concretions (CCs) in the Shajiang black soil do not change soil shrinkage behavior. • The CCs change the pore size distribution and shrinkage capacity of the Shajiang black soil. • The shrinkage curve of CC-soil mixture can be estimated from that of the fine soil. • A model is proposed for estimating the shrinkage behavior of soils containing rigid coarse inclusions. Shajiang black soil (Vertisol) has a high shrinkage capacity and contains many calcareous concretions (CC). We assume the volume of CC to be rigid during wetting and drying cycles. Thus, the soil containing CC may have different shrinkage behavior from that of fine soils (without CC). We aimed to quantify the effects of CC content and size on soil shrinkage behavior, as well as to develop a model to characterize the relationship among the void ratio (e), moisture ratio (υ), and solid volume of CC (C sv) in Shajiang black soil. Four different sizes (2–5, 5–10, 10–20 and, 20–30 mm) of the CC at a rate of 10% on mass, and four different contents (0, 5%, 10%, and 20% on mass) of 5–10 mm CCs were mixed into the fine soils to prepare the CC-soil mixtures. Our results showed that the increasing CC content significantly reduced the saturated void ratio (e s), coefficient of linear extensibility (COLE), and shrinkage index of all pores except the medium pores (P < 0.05), but the CC size did not. The shrinkage curves of the CC–soil mixtures were proportional to that of the fine soil, which was modified by the portion of CC volume in the CC–soil mixtures. We proposed a new numerical equation based on Peng and Horn shrinkage model (2005) to illustrate the relationship among e – υ – C sv. The shrinkage curve of the CC–soil mixture was predicted well (R 2 = 0.95–0.98) by the new model based on that of fine soil and the CC volume modification. However, the proposed model underestimated the volume change for the dry side of the shrinkage curve, in which the swelling and shrinkage of fine soil matrix among CCs were partially concealed. Our work demonstrates that the CC in the Shajiang black soil does not change soil shrinkage behavior except the modification of void ratio, and thus its shrinkage curve can be estimated from that of the non-CC soil. It can be concluded that this study provides a useful model for estimating the shrinkage behavior of soils containing rigid coarse inclusions. [ABSTRACT FROM AUTHOR]

We combined lab experiments, a 2-year pot experiment, light microscopy and X-ray photoelectron spectroscopic measurements to understand the fate of Fe in biochar-amended soils with, and without, three sustainable Fe-fertilization strategies (siderite, aqueous extract of Amaranthus retroflexus either alone or enriched with FeSO 4 ). In addition, we examined biochar effects on plant-available micronutrients using metal Fe. We also assessed nonlinear interactions between biochar and Fe management strategies, evaluating the effectiveness of sustainable fertilization strategies in improving Fe-nutrition of kiwifruit vines under Fe-stressed conditions. Fe chlorosis symptoms of pot-cropped kiwifruit vines were pronounced in the biochar-amended soils, especially during the first season. However, the biochar rate adopted in this study was relatively high (5 g kg − 1 w/w) while the real impact of this strategy may change at lower rates. In the lab, increasing biochar rates progressively removed dissolved micronutrients from solution. Light microscopy revealed rust-colored patches on the biochar surface exposed to a Fe source in solution and XPS analyses confirmed that the biochar surface had become coated with Fe and O in ratios consistent with the formation of Fe-(hydr)oxides. Although we investigated one specific biochar, our results suggest that some redox reactions can act to form a micronutrient sink on the biochar surface. This mechanism likely contributed to binding soil Fe (through reactive functional groups on its surface) into plant-unavailable forms, promoting the occurrence of Fe chlorosis symptoms of kiwifruit vines grown in soils amended with biochar. We also confirmed the effectiveness of siderite and A. retroflexus extract enriched with FeSO 4 in alleviating the occurrence of Fe-deficiency symptoms in kiwifruit vines. [ABSTRACT FROM AUTHOR]

Detachment of soil particles by means of raindrop impact is mainly affected by soil properties especially in the absence of vegetation cover. This study was conducted to investigate the direct and indirect effects of soil properties on splash erosion rate in calcareous soils of low vegetation cover in Lordegan region, Iran. For this purpose, Total Soil Splash (TSE), downslope (DSE) and upslope (USE) Splash erosion rate are measured under the following four conditions that comprised different values of Slope (S:%) and Rainfall Intensity (RI:mm h − 1 ): 5–50, 5–80, 15–50, 15–80, respectively, using Multiple Splash Sets (MSS). As potential estimating parameters, Surface Shear Strength (SSS), Mean Weight Diameter (MWD), Organic Matter (OM), calcium carbonate, clay content, silt and sand fractions were estimated. The effects of soil estimators on soil splash erosion rate were quantified using a path analysis and Multi-Linear Regression (MLR) approaches applied to data collected from 105 points of soil profiles (A horizon). The results showed that the particle size distribution, SSS and MWD are sensitive to some of the parameters for estimating TSE, DSE and USE rate. MWD carried the highest direct effects while SSS the highest indirect ones (via MWD) on splash erosion. Particle size effects on soil splash weren't in general observed in higher slopes and rainfall intensities. The Particle size has in general a more direct rather than an indirect effect on splash erosion. Fine silt exerted an ambivalent role on splash erosion: A high detachability of fine silt directly increases splash erosion while its capability to form a surface crust, reduces splash erosion. Indirect effect of OM through its association with MWD and SSS is more than it's direct effects. Positive direct effect of calcium carbonate is more than its indirect negative effect via its association with MWD, probably due to the presence of calcium carbonate within the size of silt and fine sand in the studied soils, causing an increase in soil detachability. [ABSTRACT FROM AUTHOR]

Under organic management soil fertility is maintained using amendments of animal manures and composts as alternatives to synthetic phosphorus (P) fertilizers. These amendments can directly affect the chemistry of soil P by altering the amounts, distribution and transformations of P forms. The amounts of various P fractions in the control and soils amended with either inorganic P fertilizer or turkey litter compost were analyzed after 1, 4, 8, 11, and 18 weeks by a sequential fractionation method. The addition of inorganic P fertilizer increased the labile/moderately labile P, while the compost increased the moderately labile P the most. Transformations of the labile/moderately labile P into more stable P occurred slowly during an 18-week incubation period. This study showed that P applied as either inorganic or organic amendments was recovered in different P fractions in a calcareous soil, and therefore it is expected that P source effects on soil P chemistry and potential for loss would differ. Fertilizer-P addition results in more labile P initially, with faster net transformation to a moderately labile form that may potentially lower the risk of P movement over time. With compost, the P enters more stable fractions initially and so it is less susceptible to loss shortly after application, but it could potentially remain a greater source of P for loss later on. [ABSTRACT FROM AUTHOR]

Soil physical quality indicators (SPQIs) are used to make complex information more accessible to decision makers; however, their site-specific nature may restrict their applicability only to a specific soil type and/or management system. Therefore, it would be advantageous if such indicators could be predicted indirectly from easily available soil properties using inexpensive methods. In this study, we introduce a hybrid algorithm, specifically designed to work with optimized decision tree with particle swarm optimization (PSO-DT), for the prediction of SPQIs (i.e., air capacity, AC; plant-available water capacity, PAWC; and relative field capacity, RFC). The potential power of using the PSO-DT algorithm in setting up a framework for identifying the most determinant parameters affecting the physical quality of agricultural soils in a semiarid region of Iran (Baft plain, 29° 11′ to 29° 13′ N and 56° 34′ to 56° 38′ E) was also investigated. An empirical multiple linear regression (MLR) model was constructed as benchmark for the comparison of performance. In results, a permutation of five input features, including soil organic matter (SOM), electrical conductivity (EC), clay, sand, and bulk density (BD), was introduced by the hybrid PSO-DT algorithm as explanatory variables. Using the PSO-DT method resulted in higher model efficiency and coefficient of determination (R 2 ) than the MLR approach. The obtained R 2 values for the constructed PSO-DT model for the AC, PAWC, and RFC predictions were 0.91, 0.90, and 0.96, respectively, whereas they were 0.61, 0.16, and 0.47 for the MLR-model. The SOM, clay, and sand parameters were accounted as the discriminating variables of the models constructed for the prediction of AC, PAWC, and RFC indicators, respectively. This study provides a strong basis for the prediction of SPQIs and identifying the most determinant parameters influencing the physical quality of agricultural soils in semiarid regions of Iran; however, its general analytical framework could be applied to other parts of the world with similar challenges. [ABSTRACT FROM AUTHOR]

Wetland restoration is globally important to reestablish functions such as carbon (C) sequestration; however, restoration activities (e.g., land clearing) can affect anaerobic C cycling and greenhouse gas production. In this study, we compared enzyme activity (ß-glucosidase) and anaerobic production of carbon dioxide (CO 2 ) and methane (CH 4 ) in soils of reference wetlands and those restored (in 2000 and 2003) by complete soil removal (CSR) after farming in an area of Everglades National Park. We found elevated gaseous production and enzyme activity in restored relative to reference wetlands. Correlations with measured activities suggest soil phosphorus (P) and C content explain site differences in C processing. We tested the potential for P and labile C limitation through direct additions of P and glucose. Production of CO 2 and CH 4 in both systems was stimulated by glucose; however, P only stimulated CH 4 production in reference wetlands. This suggests that decomposition is limited by labile C regardless of restoration, and that soil P concentrations potentially regulate CH 4 production. Additional studies are necessary to establish CH 4 production pathways and investigate the interaction between P and C availability. Following CSR, wetlands are hypothesized to shift from nitrogen (N) to P limitation; therefore, CH 4 production may decrease with restoration age while approaching P limitation. [ABSTRACT FROM AUTHOR]

Soil surface shear strength is an important input parameter in the process-based soil erosion models, but its direct measurement at the watershed scale is difficult, time-consuming and costly. This study was conducted to predict in situ shear strength of the soil surface using multiple-linear regression (MLR). The land use impact on the surface shear strength was examined as well. A direct shear box was constructed to measure in situ shear strength (cohesion, c and angle of internal friction, φ ) of the soil surface in the Semirom region located in Isfahan province, central Iran. The shear device consisted of a circular shear box (with 10 cm internal diameter and height of 1 cm), an S-shaped load cell for measuring horizontal (shear) stress and an electric motor for applying the shear stress. The normal stress acting on the failure surface was adjusted by adding weights on the shear box. Soil surface shear strength was determined using the shear box at 100 locations under three land use systems of grassland, irrigated farming and dryland farming. Soil particle size distribution (clay, silt, sand and fine clay), organic matter content (OM), carbonate content, bulk density and gravel content were determined as predictors of the surface shear strength. Normalized difference vegetation index (NDVI) was also calculated using satellite images. The MLR was employed to predict the shear strength (i.e. c and φ ) using two groups of input variables: i) easily-available soil properties (pedotransfer functions, PTFs) and ii) easily-available soil properties and NDVI (soil spatial prediction functions, SSPFs). A strong negative correlation ( r = − 0.72, p < 0.001) was found between c and φ in the studied area. Positive correlation ( r = 0.41, p < 0.001) was obtained between c and fine clay content. The c was negatively correlated ( r = − 0.31, p < 0.01; r = − 0.37, p < 0.001) with sand and gravel contents, respectively. A significant positive correlation ( r = 0.47, p < 0.001) was observed between φ and gravel content, indicating the roughness effect of coarse particles on frictional shear strength. The results also showed that NDVI is an important factor indirectly explaining the variability of both c and φ in the studied soils. The land use effect on the soil properties was investigated using the LSD 0.05 test. The means of φ somehow follow the variation of gravel content among the land uses; the highest means of clay and fine clay contents and c , and the lowest means of sand and gravel contents and φ were observed in dryland farming. The c has the same trend as did clay content; irrigated farming with the highest mean of sand content and lowest mean of clay content had the lowest mean of c . The c means were significantly different between irrigated farming and dryland farming. Prediction models of in situ shear strength derived using both soil properties and NDVI as predictors (SSPFs) were more accurate than those derived using only soil properties (PTFs). [ABSTRACT FROM AUTHOR]

Generally the direct identification of naturally occurring phosphate minerals, especially the reaction products of applied phosphate fertilizer with soil constituents, is very difficult. Nevertheless the characterization of phosphate (P) minerals and the understanding of their behavior in soils are very important with respect to fertilizer management and to safeguarding water quality. The objectives of this study were to determine the P minerals detectable in different particle size fractions of native and cultivated calcareous soils that are probably products of reactions between the soil and the fertilizer, and to examine the relationships between P mineral composition, phosphate solubility, chemical fractionation, and P activity. Fifteen calcareous soils representing four soil series were collected from native pineland and wetland, cultivated vegetable fields and fruit groves in south Florida. Soil samples were separated into sand, silt and clay with and without the removal of CaCO3 and organic matter. Mineralogy of selected fractions was determined by X-ray diffraction (XRD). Relatively distinctive crystalline apatite was identified by XRD of high-density separates from carbonate-free silt fractions of selected cultivated soils, but no phosphate minerals were detected in any fraction of the corresponding native soils. Soils were also incubated under field capacity moisture content for 30days, either without P application or with 66.8 mg P kg-1 soil applied as KH2PO4. Soil solutions were extracted and the concentrations of both anions and cations were determined. The activities of Ca2+ and H2PO4- calculated using the MINTEQA2 speciation program were adequate to support the stability of hydroxyapatite (HA), fluorapatite (FA) and tricalcium phosphate (TCP) minerals in farmed soils, while TCP was unstable in unfarmed soils, and the solution points of TCP were close to the equilibrium of HA. The results indicated that phosphate activities in native and heavily fertilized calcareous soils were controlled by the solubility of different phosphate minerals. Sequential fractionation data suggested that Ca-Mg-associated P accounted for a dominant proportion of total P in farmed soils, but this fraction was below the detectable limit in unfarmed soils. These findings demonstrate that the repeated heavy application of phosphate fertilizer during many years has resulted in the formation of stable, crystalline calcium phosphate minerals in these farmed calcareous soils. [ABSTRACT FROM AUTHOR]

Abstract: The present work was aimed at evaluating, under laboratory conditions, the medium-term influence of pepper residues applied at different rates (2, 3 and 5gkg−1) on carbon and nitrogen cycles in an agricultural soil. The cumulative quantities of CO2–C that evolved from the pepper residue mineralization were fitted to a first-order kinetic model. These values are equivalent to ~30% of the organic carbon added for all doses, with similar mineralization constant rate (~0.09days−1). Net ammonification followed the same pattern in all doses indicating a net loss of NH4 +–N by nitrification or immobilization. Net nitrification followed a different pattern depending on the dose. Final positive values were observed for the two highest doses, but when 2gkg−1 was applied, net nitrification was always negative, suggesting net immobilization of N. The net N mineralization was −3.1, 13.7 and 56.7mgkg−1 for doses 2, 3 and 5gkg−1, respectively. Thus, the addition of pepper residues at low doses produced a net N immobilization in soil. This trend may indicate that N is likely a limiting factor for microbial growth. The activities of soil enzymes involved in C and N cycles responded differently according to the dose, indicating that only the highest dose would increase the capacity of soil to perform useful ecosystem functions. These results highlight the importance of dose when applying pepper residues, since doses <5gkg−1 do not easily release available N for plant growth in the loamy calcareous soil used for this experiment. [Copyright &y& Elsevier]

[Display omitted] • Al compounds were the most dominated soil solid phase P species in acidic soils. • Ca and Al compounds dominated the soil solid phases P species in high pH soils. • Soil pH was the critical controller for P species and solubility. • Dissolvable-colloidal-Fe/Al phases might be bioavailable under acidic conditions. • DGT technique could explain soil-plant P concentration. Soil solid-phase phosphorus (P) speciation and chemical conditions exert a crucial role in both aqueous P speciation and concentration—the most available and mobile pool for biota in environments. However, the interplay between solid-phase speciation and the aqueous phase of P in soil systems is unresolved. Herein, we investigated the speciation and solubility of P in tropical agricultural soils, which are often poor in P availability. Phosphorus K -edge X-ray absorption near edge structure (XANES) spectra of acidic soils identified dominant Al-hydroxide-phosphates (∼58%: P adsorbed to gibbsite 19%, P adsorbed to kaolinite 14%, and variscite 16%), followed by Fe-hydroxide-phosphates (∼36%: P adsorbed to ferrihydrite 14% and strengite 22%), and trace organic P (∼6%). Calcium phosphates (∼52%) prevailed in the alkaline/calcareous soils with moderate and minor contributions from Al-phosphates (∼37%: P adsorbed to kaolinite 28%, P adsorbed to gibbsite 1%, and variscite 7%) and Fe phosphate (∼11%), respectively. The time-averaged P concentration in the aqueous phase using diffusive gradients in thin films (C DGT) was highly variable from 4 to 123 μg P L–1, with the highest and the lowest values observed in acidic-coarse- and alkaline-fine-textured soils, respectively. The C DGT concentration was positively related to belowground P uptake. The C DGT concentration had negative relationships with pH, Ca-P XANES, and total and extractable Ca, indicating that Ca phosphates were the primary constituents decreasing the dissolvable P concentration. This study highlighted the importance of solid-phase P species in determining P fluxes and is relevant to diverse soils rich in Fe/Al/Ca compounds under extremely acidic to alkaline conditions. [ABSTRACT FROM AUTHOR]

• Saturation potentials for SOC in Lower Austria exceed that of many other regions. • Carbon deficits are controlled by soil properties and land use. • Highly variable SOC status among Lower Austrian regions and WRB soil groups. • Recent SOC accumulation not related to saturation deficits but management changes. Policies for restoring soil health and mitigating climate change require information on soil organic carbon (SOC) stocks and their spatial and temporal variation, and related sequestration potentials. Using the province of Lower Austria as environmentally diverse model region, we present a detailed analysis of SOC stocks, saturation potentials and deficits along with SOC monitoring data for the past three decades. Using the provincés soil database (sampling 1991) we estimated the saturation potential for mineral-protected C (C sat) by boundary line regression to the particle fraction <20 µm (f < 20µ m). Compared to published work, parameterization by Lower Austrian data yielded considerably larger C sat values which agree well with independent maximum organic C load estimates based on specific surface area. C sat is particularly small in topsoils of regions with non-calcareous igneous rock, but large on fine-textured quaternary and tertiary sediments, and weathering residuals of carbonate rock. During the past three decades, the medians of SOC in grassland topsoils (0–20 cm) increased significantly (p < 0.05) by 29.7% from 39.4 to 51.1 g kg−1, corresponding to annual accumulation rates of 0.87 Mg C ha−1. SOC in cultivated soils increased by 17.1% from 12.7 to 14.8 g kg−1 (0.20 Mg C ha−1 y−1). Because of the large initial C gap, the observed SOC accumulation is not related to C def but likely reflects improved soil management. [ABSTRACT FROM AUTHOR]

Abstract: A set of periurban calcareous agricultural Mediterranean soils, with a natural gradient in the content and composition of organic matter (OM), was spiked with a mixture of Cd, Cu, Pb and Zn at two levels – designated Tt1 and Tt2 – within the limit values proposed by the current European legislation and incubated for ≤12months. We conducted bioassay experiments with romaine and iceberg varieties of lettuce (Lactuca sativa L.). Metal bioavailability patterns were evaluated as a function of soil constituents and extractable metals. Metal contamination produced a decrease in plant biomass (up to 50%) and nutrient imbalance. The redundancy analysis showed that the carbonate, OM and fine mineral fractions account for up to 85% of the variance in metal bioavailability patterns in lettuce plants. Carbonate and fine mineral fractions were negatively related to Cd and Zn bioavailability in plants respectively. Organic matter explained Cu and Pb bioavailability, although patterns varied between plant tissues according to their organic composition. The labile fraction limited metal absorption of Pb by roots at the Tt2 level and Cu at both levels, but Cu and Pb translocation was enhanced at both levels. There were significant correlations between metals in leaves and metals extracted with both neutral salts and complexing agents. The high rate of metal translocation and the considerable influence of soil properties may indicate that the limiting values of metals in soils proposed by the current European legislation should be revised in the case of multi-component systems, and/or be established according to the soil characteristics. [Copyright &y& Elsevier]

Abstract: Agricultural manures are the source of several pathogenic microorganisms in surface and groundwater that could cause diseases and adversely affect human health. Some strains of E. coli, an indicator microorganism, when transported over and/or through the soils reaching the water resources, cause urinary tract infections, diarrheal diseases, and contribute to infant mortality, fatal renal or neurological complications. To the best of the authors' knowledge, there is no information about the bacterial transport through natural/intact calcareous and gypsiferous soils. In this study, we selected four soil types to investigate the influence of lime and gypsum content on transport and filtration of E. coli released from cow manure during saturated and unsaturated flows. Intact soil columns from Hamadan and Isfahan provinces in Iran were transported to the laboratory. Cow manure was applied to the surface of each column at a rate of 10Mgha−1 dry basis. Soil columns were leached up to four pore volumes (PVs) at 20°C. E. coli influent (C o) and effluent (C) concentrations were measured by the plate-count method and C o/C values were drawn vs. PV as breakthrough curves (BTCs). Filtration coefficient (λ f), relative adsorption index (S R), and maximum depth of potential contamination (Z max) were calculated as indices of filtration and transport processes. Our results illustrated that contamination of water is possible where flooding irrigation systems occur in the low-lime soil due to low ionic strength and salinity, and greater structural stability. The BTCs showed that preferential pathways are greater in the low-lime soils than in the other studied soils. The presence of the natural lime and gypsum affected solution chemistry, macro and microporosity of the studied soils, which resulted in more bacterial filtration. The soils high in lime and gypsum also had maximum values for λ f and S R, respectively. Minimum Z max was observed in the high-lime soil and its mean was significantly lower than in the three other soils. The Z max was greater in saturated flow conditions than in unsaturated flow conditions. Overall, when a source of E. coli (e.g. cow manure) is applied on a low-lime or gypsum soil, subsurface water contamination would be expected while high-lime and gypsum soils could filter more bacteria. This study showed the effect of natural lime and gypsum on bacterial transportation through intact soils. It is suggested to use techniques such as scanning electron microscope (SEM) and image analysis to present pore-scale information for bacterial movement through calcareous and gypsiferous soils. [Copyright &y& Elsevier]

[Display omitted] • The four most widely used lab methods for soil organic matter (OM) were compared. • Not only the fine earth but the silt-plus-clay was studied. • How the conversion coefficients between methods are related was revealed. • The conversion coefficients depend on OM quality chemical characteristics. • These OM characteristics are related to its stoichiometry and oxidation resistance. Nowadays, the continuous organic carbon (OC) assessment in soil and its various particle-size fractions is needed to correctly estimate the soil organic matter (OM) contents and dynamics. However, the existence of several widely used analytical methods for OC and OM determination hinders the comparison of OC and OM data taken by different laboratories, in different times, soil classes, horizons and particle-size fractions. Although these methods are usually related by means of empirical soil-dependent factors, how these coefficients vary among soils is seldom addressed. In the present work 67 samples from the A horizons (0 to 20–40 cm depth) of 58 forest and agricultural calcareous soils from the Valencia province (Eastern Spain) were taken, the silt-plus-clay separated, and both the fine earth and the silt-plus-clay analysed through the wet dichromate self-heated and externally heated oxidations, the dry combustion with CO 2 measurement and the loss-on-ignition. As a consequence, the readily oxidizable carbon (RXC), the total oxidizable carbon (TXC), OC and OM were obtained, respectively. Furthermore, the coefficients to convert among these properties, namely, the Walkley-Black factor (f WB), the oxidation recovery factor (f XR), the carbon valence in the organic matter (v C,OM), and the van Bemmelen (f VB) factor were assessed. The RXC in both fine earth and silt-plus-clay was 75% of the OC thus supporting a common f WB of 1.33. However, the OM in the fine earth presented less f XR than the silt-plus-clay. This apparent inconsistency between f WB and f XR was caused by the different v C,OM in the fine earth (3.45) and the silt-plus-clay (4.56) and hence, the different oxidation state of the OC in each fraction. This was revealed by how f WB depends on f XR and v C,OM through f WB = 4 f XR / v C,OM. Therefore, the different v C,OM exactly compensated for the different f XR in each fraction to give the same f WB for both. Besides, the different v C,OM in each fraction was consistent with the fact that carbon accounted for 61% and 71% of the OM mass in, respectively, the fine earth and the silt-plus-clay, thus supporting the use of a van Bemmelen factor below the standard of 1.72 and different, i.e., 1.64 and 1.41, for each particle-size fraction. This fact can be understood taking into account that v C,OM linearly depends on f VB through v C,OM = 4 – α – β f VB , where α and β are two empirical coefficients. Therefore, it has been shown how the conversion coefficients among the RXC, TXC, OC and OM depend on two independent chemical characteristics, one OM-stoichiometry-related, the carbon mass fraction, and another OM-reactivity-related, the oxidation recovery. As a consequence, it will be better understood that the determinations of OC and OM in soils, remarkably when the Walkley-Black method is used, vary not only because of changes in OC and OM magnitude, but also because of changes in OM stoichiometry and reactivity. The differences in the soil OC and OM data obtained by using different laboratory methods, and in different times, particle-size fractions, soil depths, classes, etc., will be thus better understood. [ABSTRACT FROM AUTHOR]

• Calcium solubilization was higher from dolomite than limestone. • High amounts of gluconic acid caused higher Ca solubilization from dolomite. • Gross P solubilization was higher from P-poor dolomite than from P-rich limestone. • The abundance of P-solubilizing bacteria was higher in the P-poor than in P-rich soil. • Pseudomonadales and Enterobacteriales were the dominant P-solubilizers in alkaline soils. Phosphorus (P) availability in calcareous forest soils is commonly low compared to siliceous soils. The main reason for this is that phosphate ions tend to precipitate with calcium (Ca). Weathering of calcareous rocks and the potential of microorganisms to dissolve calcareous parent material is not fully understood. Therefore, we examined microbial carbonate dissolution and the abundance of phosphorus-solubilizing bacteria in temperate forest soils with contrasting calcareous parent materials. We incubated soil extracts with weathered parent materials (i.e., dolomite and limestone) from two calcareous forest soils differing in P content and determined the rates of P and Ca solubilization. In addition, we determined the abundance of phosphorus-solubilizing bacteria (PSB). We found that the net Ca solubilization rate ranged from 8.8 to 511.1 nmol m−2 d−1 across both soils and depths. Calcium dissolution rates were negatively related to pH and positively related to the concentration of organic acids. The gross P solubilization rates were on average 63.6% higher from dolomite (P-poor soil) than from limestone (P-rich soil). The abundance of soil PSB ranged from 3.8 % at the limestone site (P-rich soil) to 24.4 % at the dolomite site (P-poor soil). The higher abundance of PSB in the soil derived from dolomite is in line with the high Ca and P solubilization rates at this site, indicating that PSB abundance is related to rock weathering rates from calcareous soils. Pseudomonadales and Enterobacteriales were by far the two most abundant bacterial orders in the PSB community of both soils and soil depths. In conclusion, this study shows, first, that weathering of calcareous bedrocks is strongly affected by the activity of soil microorganisms, and second, that there is likely a selective pressure in P-poor soils towards a higher abundance of PSB. [ABSTRACT FROM AUTHOR]

The speciation and availability of phosphorus fertilizer when applied in highly concentrated bands is influenced by both the form of fertilizer and soil properties. [Display omitted] • We examined phosphorus (P) speciation in highly concentrated fertilizer bands. • In non-calcareous soils, precipitation of aluminum-P regulated P availability. • In a calcareous soil, precipitation of calcium-P regulated P availability. • Soil properties and the form of P are critical for fertilizer strategies. The factors affecting chemical transformations of phosphorus (P) in highly concentrated fertilizer bands have received little attention, with no previous studies having utilized in situ approaches to examine these changes in P speciation within the fertosphere. In the present study, an incubation experiment was conducted to examine the impact of soil properties, the form of P and the co-application of K on changes in P speciation in highly concentrated fertilizer bands. In non-calcareous soils, the precipitation of P as Al-P minerals was found to be critical, with decreases in pH increasing solubilization of soil Al, increasing the precipitation of Al-P minerals, and hence markedly decreasing potential P availability. As a result, factors altering pH, including soil properties and the form of the P fertilizer, are important in determining P availability through regulation of Al-P precipitation. In a calcareous soil, P availability was greatly reduced due to precipitation of Ca-P minerals. The co-application of K resulted in comparatively subtle changes in P speciation, being most pronounced in soils with a high cation exchange capacity, likely by altering Ca- and Mg-P precipitation. The finding that soil properties and the form of P supplied were more important than the co-application of K in controlling P solubility indicates that optimizing P form is important when designing fertilizer placement strategies. [ABSTRACT FROM AUTHOR]

• P leaching was evaluated in a flooded calcareous soil. • Ammonium combined with straw incorporation increased P leaching by Fe(III) reduction. • Acid elution combined with straw incorporation reduced P leaching in flooded calcareous soil. • Straw incorporation had no effect on P leaching in flooded calcareous soil. Straw incorporation (SI) coupled with ammonium nitrogen (AN) application is a management strategy for storing organic carbon (OC) and optimizing vegetable yields in intensively managed calcareous soils of North China. However, during short term flooded conditions, the resulting soil acidification and subsequent Fe reduction processes may affect the transformation of soil Fe/Al-bound phosphorus (Fe/Al-P) and the mobility of phosphate in soil. This study was conducted simulating the condition of short term flooding in order to investigate P leaching and the contents of soil inorganic P fractions, Fe(III) reduction and P adsorption kinetics in calcareous soil with four treatments; control (C), straw powder incorporation (SI), SI with subsequent AN elution (SN) and SI with subsequent sulfuric acid elution (SH). The results showed that the SI treatment promoted the transformation of Ca-bound P (Ca-P) in soil to Fe/Al-P due to acidification but had no effect on P leaching. The SN treatment significantly decreased the topsoil Fe/Al-P content and maximum P sorption capacity through Fe(III) reduction, whereas it increased the total amount of P leached under flooded conditions by 86.8%. In contrast, SH promoted Fe/Al-P accumulation as well as increase the soil maximum P sorption capacity in the topsoil, leading to a decrease in P leachate of 38.1% compared with the SI treatment. The SN treatment was responsible for high P mobility through promotion of Fe(III) reduction and inhibition of acidification processes. Such findings in the present study highlight that 1) SI coupled with AN induced the Fe(III) reduction releasing associated P while 2) SI coupled with acidification significantly inhibited the P leaching, which is of environmental benefit. However, the results presented herein were limited to a single soil type. Future studies should validate the processes found in the present study across other soil types. [ABSTRACT FROM AUTHOR]

• Vis-NIR spectra coupled with SVR algorithm were used to predict TFV. • Extensive in-situ wind tunnel experiments and soil analysis were performed. • Key wavelengths were introduced for the prediction of TFV. • The derived PSTF outperformed the PTF for the TFV estimation. • Results of our study can be used for TFV mapping on regional and global scales. Wind erosion potential can be assessed using the Threshold Friction Velocity (TFV) of the soil, which is not always easy to measure, especially on regional and global scales. To overcome this difficulty, the spectroscopy technique can provide a useful approach in estimating the TFV as an alternative for time-consuming wind tunnel studies in the field. In this study, we evaluated the potential of Vis-NIR spectroscopy in predicting the TFV and some TFV-related soil properties using Partial Least Square Regression (PLSR) and the Support Vector Regression (SVR). We also developed a Point Spectrotransfer Function (PSTF) using Multiple Linear Regression (MLR) to predict the TFV based on diagnostic wavelengths and compared it to the derived Pedotransfer Function (PTF). For this purpose, 300 in-situ wind tunnel tests were performed in the Fars Province, Iran and the spectral reflectance of soil samples were analysed using a spectrophotometer apparatus. The 10 best key wavelengths resulting from the correlation analysis between the TFV and the spectral reflectance were 750, 1342, 1446, 1578, 1746, 1939, 2072, 2162, 2217, and 2338 nm which were mostly located in the short-wavelength infrared (SWIR) area. The derived PSTF performed better than the PTF for the TFV estimation (R2 = 0.94, RMSE = 0.71). Results of the predictive models revealed that machine learning using the SVR had a significantly (P < 0.01) higher prediction accuracy for the TFV estimation (R2 = 0.85, RMSE = 0.45, RPD = 2.50, and RPIQ = 4.06) than the PLSR (R2 = 0.68, RMSE = 1.01, RPD = 1.72, and RPIQ = 2.64). The same results were obtained for the soil moisture, clay and CaCO 3 content. This study proved that reflectance spectroscopy coupled with the machine learning algorithm is a promising technique for large-scale assessment of wind erosion. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we modified a spray method to visualize iodide water tracer in calcareous soil with high pH, and developed a process to combine multiple soil horizontal sections to establish three-dimensional (3-D) visualization modeling for water-flow paths in soil. In the modified spray method, pH adjuster was misted onto the soil surface to lower soil pH after starch solution with oxidizer (ferric ion) had been sprayed onto the soil profile irrigated by iodide-labeled water. The acidic condition accelerated the distinct purple–blue color of iodine–starch. When images of multiple soil horizontal sections stained by iodine–starch complex were captured by digital camera, the iodine–starch color stained pattern on the soil surface was outlined using software ImageJ (developed at the US National Institutes of Health). After all 3-D coordinates were outlined with dots, 3-D visualization modeling for water-flow paths in soil was established using software Surfer 8.0 (Golden Software Inc.) as an alternative method for studying water infiltration and distribution behavior in soil. [Copyright &y& Elsevier]

Abstract: The two most widely used modern soil classification schemes are Soil Taxonomy (ST) and World Reference Base for Soil Resources (WRB). The purpose of this paper is to clarify the differences and highlight the similarities between ST and WRB in their current state, with special emphasis on calcareous soils in arid and semi-arid regions of Iran. Four study sites were selected from central, northeast, and southeast Iran, and four representative pedons were described and classified for each site. Then, soil units from WRB were compared to those obtained by using ST at the family level. The results demonstrated that WRB shows more accessory soil properties compared to ST; moreover, through the method of combining qualifiers, the WRB system is a better option for naming calcareous soils. Defining new great groups, including Natrisalids, Gypsisalids, Calcisalids, Gypsicalcids, and Calcixeralfs, and new subgroups consisting of the Calcic Natrisalids and Calcic Natrargids for ST, and the “Paralithic” qualifier for the WRB system, could increase the usefulness and correlation between these two soil classification systems. Moreover, the definition of some reference soil groups (such as Vertisols), diagnostic horizons (such as salic), and/or qualifiers (such as Luvic prefix) should be revised to harmonize the classification systems. [Copyright &y& Elsevier]

Abstract: Preservation and restoration of wetlands is critical to maintain their key functional roles of improving water quality, carbon sequestration, and mitigation of greenhouse gas emissions. Restoration of former agricultural wetlands often requires severe measures including removal nutrient-enriched soil followed by natural succession involving changes in nutrient storages and transformations. The focus of this study was to assess changes in biogeochemical parameters during the early stages of soil development following complete soil removal in a calcareous subtropical wetland. Results indicated that significant changes occur in the first 16years including increased soil depth, accumulation of organic matter, carbon (C), nitrogen (N), and phosphorus (P). Early development of soils showed a shift from initial N limitation towards a state of co-limitation by N and P after 16years. Functional responses of these changes were determined by monitoring the microbe-driven processes (enzyme activities and soil oxygen demand) with respect to the nutrient changes. Soil β-glucosidase activity increased in the first few years and then declined with age of the soils. Alkaline phosphatase activity was inversely correlated to the P concentration in soils. When compared with an undisturbed reference site, these parameters indicate that N processes recover more rapidly than those of P and C, but functional attributes related to P limitation should begin to mimic restored conditions within the next century. [Copyright &y& Elsevier]

Abstract: Water extractable organic matter (WEOM) in soil refers to a broad mixture of water-soluble structures recoverable in laboratory through predetermined procedures. In this work, we investigate the mechanisms controlling the occurrence of WEOM fractions isolated on XAD-8/4 resins in a calcareous soil profile as a function of soil depth and seasonal climatic changes. WEOM was roughly collected on a bi-weekly basis during eight consecutive months from an experimental field in the Mediterranean region, south-east of France. Each fraction was analysed for organic carbon content and further characterised using UV/Vis absorbance and 3D fluorescence spectroscopy. The concentrations of hydrophobic (HPOA), transphilic (TPIA) and hydrophilic (HPIA) acids fractions isolated from WEOM followed similar decreasing trends with increasing soil depth, but HPOA decreased most sharply. Specific UV absorbance at 254nm (SUVA254) indicated that HPOA''s distribution along the soil column is strongly influenced by the selective removal of aromatic structures, which could be controlled by adsorption mechanisms involving organo-mineral interactions and/or by a shift towards less aromatic precursors in deeper soil layers. 3D spectra of fluorescence revealed the presence of four types of fluorophores: two humic-like (A and C) common to all fractions, one lignin-like (H) specific to HPOA particularly in the upper soil layer, and two protein-like (B1 and B2) specific to TPIA. The importance of the humic component in all fractions was verified by the highly significant correlations between their carbon content and the intensity of humic-like peaks. The aging index (IA/IC) and the fluorescence index (FI), two indicators derived from 3D fluorescence spectra, showed an increase in the microbial input and the degree of humification in HPOA as a function of increasing soil depth. By comparison, IA/IC and FI values in HPIA and TPIA indicated that both fractions were composed almost exclusively of microbial-derived structures, regardless of soil depth. Principal component analysis (PCA) showed the association of temperature (T) to the carbon content in all fractions extracted from the soil layers 0–30 and 30–60cm, suggesting possible role of microbial activity on their occurrence. The hydraulic regime in soil, controlled by the frequency of rainfall events, affected most significantly HPIA across the entire soil column. PCA, however, failed to identify any consistent trends relating the qualitative properties of WEOM fractions to climatic variables. [Copyright &y& Elsevier]

Abstract: FeEDDHA (iron (3+) ethylenediamine-N,N′-bis(hydroxy phenyl acetic acid) products are commonly applied to mend or prevent Fe chlorosis in plants. In soil application, racemic and meso o,o-FeEDDHA are the effective components, while o,p-FeEDDHA tends to adsorb or react to o,p-CuEDDHA. Upon interaction with soil, a plant-independent, gradual decline in soil solution concentration of meso o,o-FeEDDHA and o,p-CuEDDHA has been observed. The aim of this study was to examine to what extent biodegradation contributes to this gradual decline. A 4-week incubation experiment was done with calcareous soil to which FeEDDHA was added. The experiment involved three sterility regimes, two conditioning regimes and three time steps. Soil solution concentrations of meso o,o-FeEDDHA and o,p-CuEDDHA gradually declined in all sterility regimes. Biodegradation did not significantly contribute to the decline in concentration of any EDDHA chelate, except for CoEDDHA, which was formed in small quantities as a result of cation displacement. The rate of the process causing the decline in meso o,o-FeEDDHA and o,p-CuEDDHA concentration was higher at higher temperature and in soil not exposed to gamma irradiation. This study offers no evidence that the effectiveness of soil-applied FeEDDHA fertilizers is compromised by biodegradation. [Copyright &y& Elsevier]

Abstract: Enzymes are able to be sorbed and immobilized by clay minerals and humic colloids in soil environments. The present study was done to elucidate the effects of soil innate carbonates on the sorption, immobilization and activity of cellulase in a calcareous soil by treating it with different levels of acetic acid. The study of adsorption isotherm revealed that soil carbonates removal with acetic acid increased the intensity of cellulase adsorption (1/n) estimated by the Freundlich model. Based on the Freundlich isotherm model it is predicted that cellulase molecules will be increasingly adsorbed on acetic acid treated soil with increasing cellulase concentration. However, practically the amounts of cellulase protein adsorbed and immobilized on untreated soil with high levels of ECC were significantly higher than those on acetic acid treated soils. The immobilized cellulase activity and particularly its specific activity decreased considerably with increasing carbonate contents in soil. [Copyright &y& Elsevier]